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Most biologically natural compounds are very sensitive and easily degradable under drying conditions. This study aimed to investigate the effect of drying temperature on the contents of phenolic compounds and in vitro antioxidant and antidiabetic activities of wild guava leaves. Wild guava leaves were dried at 40 °C, 50 °C, 60 °C, 70 °C, and 80 °C, as well as sun drying (SD). The total phenolic and flavonoid contents (TPC and TFC) were measured using the colorimetric method. Antioxidant activity was determined by the 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) and 2,2-azino-bis(3-ethylbenzothazoline-6-sulfonic acid (ABTS) radical scavenging activity assays. In vitro antidiabetic activity was measured by assessing α-glucosidase and α-amylase inhibitory activities. The contents of individual phenolic compounds were determined using ultra-performance liquid chromatography (UPLC). The principal component analysis (PCA) results revealed that hot air drying at different temperatures had significantly different effects on the bioactive compounds and biological properties of guava leaves. Drying at high or low temperatures resulted in a higher degradable rate of bioactive compounds leading to a weakening of the biological properties. Drying at 50 °C resulted in high TPC and TFC as well as the highest in vitro antioxidant and antidiabetic activities. Furthermore, the highest contents of gallic acid, catechin, rutin, quercetin, apigenin, quercitrin, vitexin, and apigenin-7- O-D-glucopyranoside were found in samples dried at 50 °C, whereas the highest contents of chlorogenic acid, epicatechin, and ellagic acid were observed in samples dried at 60 °C. Therefore, drying at 50 °C was the suitable temperature for retaining valuable biological compounds in wild guava leaves.

Syzygium zeylanicum (L.) is a common medicinal herb distributed in Asian countries and has been reported to possess significant antioxidant and antidiabetic activities. In this study, ethanolic extract from this plant was encapsulated by spray drying using resistant maltodextrin and its blends with gum Arabic, α‐cyclodextrin, β‐cyclodextrin, and γ‐cyclodextrin coating materials. The physical characteristics, antioxidant and antidiabetic activities, and phenolic release kinetics of the obtained microcapsules were evaluated. All coating formulations used for spray drying resulted in spherical microcapsules with high encapsulation efficiency and water solubility index. The single use of resistant maltodextrin showed the greatest release of phenolic compounds from microcapsules as well as antioxidant and antidiabetic capacities compared to the other blending formulations. Thus, resistant maltodextrin is suggested to be used as the coating agent to produce encapsulated powder containing Syzygium zeylanicum L extract which will be further supplemented into food and pharmaceutical products. Novelty impact statement Bioactive ingredients extracted from Syzygium zeylanicum (L.) were successfully encapsulated with resistant maltodextrin by spray drying for the first time. The obtained phenolic‐rich microcapsules with high water solubility index and significant antioxidant and antidiabetic activities may be applied as a functional supplement for foods and pharmaceutical products.

Syzygium zeylanicum L. (DC) (SZL) has been used in antidiabetes treatment for ages. However, the scientific evidence of active agents that have antidiabetic activity and response against biological activities is limited. In this study, the active components of SZL trunk‐bark extract (SZL extract) were identified using principal component analysis (PCA), and their antidiabetic activities were assessed. The results indicated that the ethyl acetate fraction (EAF) had the highest concentration of phenolic compounds, antioxidants, and antihyperglycemic activities in the postprandial zebrafish model. The major antioxidant contributors were gallic acid, catechin, epicatechin, ellagic acid, quercetin, caffeine, and apigenin, and their concentrated levels reduced α‐amylase inhibitory activity, whereas rutin and ethyl gallate influenced the α‐glucosidase inhibitory activity. This study showed the bio‐functional properties of active phenolic compounds present in the SZL extract, potentially serving as a functional food to control hyperglycemia.

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